The present invention relates generally to data transmission in mobile communication systems and more specifically to a system and method for intra-cell frequency reuse in a communications network including one or more relay nodes.
As used herein, the terms “user equipment” and “UE” can refer to wireless devices such as mobile telephones, personal digital assistants (PDAs), handheld or laptop computers, and similar devices or other User Agents (“UAs”) that have telecommunications capabilities. A UE may refer to a mobile, or wireless device. The term “UE” may also refer to devices that have similar capabilities but that are not generally transportable, such as desktop computers, set-top boxes, or network nodes.
In traditional wireless telecommunications systems, transmission equipment in a base station transmits signals throughout a geographical region known as a cell. As technology has evolved, more advanced equipment has been introduced that can provide services that were not possible previously. This advanced equipment might include, for example, an evolved universal terrestrial radio access network (E-UTRAN) node B (eNB) rather than a base station or other systems and devices that are more highly evolved than the equivalent equipment in a traditional wireless telecommunications system. Such advanced or next generation equipment may be referred to herein as long-term evolution (LTE) equipment, and a packet-based network that uses such equipment can be referred to as an evolved packet system (EPS). Additional improvements to LTE systems/equipment will eventually result in an LTE advanced (LTE-A) system. As used herein, the phrase “base station” or “access device” will refer to any component, such as a traditional base station or an LTE or LTE-A base station (including eNBs), that can provide a UE with access to other components in a telecommunications system.
In mobile communication systems such as E-UTRAN, a base station provides radio access to one or more UEs. The base station comprises a packet scheduler for dynamically scheduling downlink traffic data packet transmissions and allocating uplink traffic data packet transmission resources among all the UEs communicating with the base station. The functions of the scheduler include, among others, dividing the available air interface capacity between UEs, deciding the transport channel to be used for each UE's packet data transmissions, and monitoring packet allocation and system load. The scheduler dynamically allocates resources for Physical Downlink Shared CHannel (PDSCH) and Physical Uplink Shared CHannel (PUSCH) data transmissions, and sends scheduling information to the UEs through a scheduling channel on the Physical Downlink Control CHannel (PDCCH). In some cases, control information is communicated from the UE to the base station using the Physical Uplink Control CHannel (PUCCH) or PUSCH.
Generally, communications between a base station and UE are contained within one or more resource blocks (RBs). The RBs provide a structure for encapsulating data within particular timeslots or symbols that are transmitted by either the base station or UE at particular times. An exemplary RB may include, for example, several Resource Elements (REs) that are arranged in frequency columns and time rows as known in the art. In that case, each RE corresponds to a different time/frequency combination for data to be transmitted between a base station and UE.
Hybrid Automatic Repeat reQuest (HARQ) is a scheme for re-transmitting a traffic data packet to compensate for an incorrectly received traffic packet that is communicated between a base station and UE. A HARQ scheme may be used both in uplink and downlink. Take downlink transmissions for example, for each downlink packet received by a UE, a positive acknowledgment (ACK) is transmitted on, for example, a PUCCH, from the UE to the base station after a cyclic redundancy check (CRC) performed by the UE indicates a successful decoding. If the CRC indicates a packet is not received correctly, a UE HARQ entity transmits a negative acknowledgement (NACK) on, for example, the PUCCH, in order to request a retransmission of the erroneously received packet. Once a HARQ NACK is transmitted to a base station, the UE waits to receive a retransmitted traffic data packet. When a retransmission request is received at a base station, the base station retransmits the incorrectly received packet to the UE. This process of transmitting, ACK/NACK and retransmitting continues until either the packet is correctly received or a maximum number of retransmissions has occurred.
In some LTE radio access networks (RANs), relay nodes (RNs) may be incorporated into the network to improve cell edge performance and increase average cell throughput. For example, FIG. 1 is an illustration of an exemplary network architecture including RNs positioned around a cell edge. As shown in FIG. 1, network 100 includes base stations 102 and 104. Base stations 102 and 104 are each in communication with mobile management entity (MME)/serving gateway (SGW) 106 and 108 for providing core network functionality. In some cases, one or more UEs (e.g., UE 110) may be in direct communication with either of base stations 102 and 104 (either concurrently or at different times). In other cases, however, when one or more UEs cannot establish a strong connection with either base station 102 or 104, the UEs may, instead, communicate using one or more of RNs 112, 114, 116, or 118. For example, as shown in FIG. 1, UEs 120, and 122 are each communicating with an RN rather than a base station directly. When communicating with an RN, the data the RN receives from the UE is forwarded to an available base station for processing. Conversely, data received by an RN from a base station that is allocated to a particular UE is forwarded to that UE by the RN. Accordingly, in this configuration, UEs may be able to access network resources at a higher data rate and/or with lower power consumption using RNs.
Different types of RNs may be defined depending upon the functional capabilities of the RN. A Type I RN is essentially a small base station with a lower transmit power, e.g., 30 dBm, and in-band wireless backhaul. Conversely, a Type II RN does not create a new cell and only facilitates data transmission and reception for a particular base station. Generally, Type II relays do not have a separate Physical Cell ID and do not create any new network cells. Also, Type II relays are transparent to Rel-8 UEs. As such, a Rel-8 UE is not aware of the presence of a type II RN. Type II RNs can transmit PDSCH, but do not transmit cell-specific reference signals (CRS) or a PDCCH. CRS may be used by a UE communicating with a base station to determine channel characteristics and to allow the base station to schedule packet transmissions according to those channel characteristics. By comparing a received CRS to known reference signals (i.e., known data), a UE can determine channel characteristics (e.g., a channel quality index, etc.). The difference between the known data and the received signal may be indicative of signal attenuation, path-loss, interference level, noise, etc.
When implementing networks incorporating RNs, it may be possible to provide more efficient coverage and/or higher capacity if one or more of the base station and associated RNs can each use the same resources simultaneously to provide services to connected UEs. If the radio coverage of the RNs and base station overlap, however, it may be difficult to reuse resources as the overlapping coverage may result in significant interference.